In a portable communications device, such as a wireless cellular telephone, it is desired for the device to be capable of receiving signals from a remote transmitter at all times. Thus, while the communications device is in a quiescent mode, in which the device is not actively engaged in a telephone call, the device must be capable of receiving ring alerts or pages from the remote station. Additionally, while the device is actively engaged in a telephone call, it must be capable of receiving and transmitting to the remote station.
When a wireless cellular telephone is actively engaged in a telephone call, the device is typically operated while in an upright orientation, consistent with a standing or seated posture of the particular user. Because of the relatively predictable orientation of the cellular telephone, any communications antenna used by the telephone to receive and transmit signals can be optimized to operate in the particular orientation. In a terrestrial cellular telephone, for example, the radiation pattern of the antenna is generally optimized to receive signals from and transmit signals to a remote station located near a 0 degree elevation angle relative to the user. Additionally, there is usually little need for significant antenna gain at large elevation angles.
In contrast, when a wireless cellular telephone is in a quiescent mode, the telephone may be oriented in any particular direction. Thus, the telephone may be placed on a horizontal surface corresponding to a countertop or the dashboard of an automobile, or may be in an upright position by way of a clip on the belt of a user. Thus, any communications antenna used by the telephone to receive and transmit signals must be capable of receiving signals from any direction. If the antenna is not capable of receiving signals from any particular direction, this results in the user not receiving calls which are directed to him or her. Additionally, as wireless cellular telephones continue to decrease in size, the antenna used within the telephone should require minimal volume in the quiescent mode with the antenna confined to a stowed position. When the telephone is actively engaged in a call, the antenna should extend in a telescopic fashion to a maximum length in order to ensure that the head of the user does not interfere with the radiation pattern of the antenna.
These constraints on the design of the antenna can be especially problematic when the portable communications device is a satellite cellular telephone. In a satellite cellular communication system, the satellite cellular telephone must be capable of receiving relatively low power signals which are transmitted from an orbiting satellite. This increases the gain requirements of the antenna used within the satellite cellular telephone, and increases the difficulty in conveying ring alerts from the satellite to the telephone. Additionally, when the satellite cellular telephone is actively engaged in a telephone call, the bulk of the energy transmitted by the telephone must be directed upward, where communications satellites are expected to be located.
Therefore, it is highly desirable for a portable communications devices, such as a satellite cellular telephone, to incorporate a telescopic antenna which possesses a dual radiation pattern. Such an antenna would allow reliable reception of ring alerts while the telephone is placed in a quiescent mode, and at any orientation, as well as provide reliable reception and transmission of communication signals from orbiting satellites while the user is actively engaged in a telephone call.